The present invention relates generally to systems and methods for three-dimensional mapping and reconstruction, and specifically to mapping and reconstruction of the interior of body organs, such as the heart.
Methods for three-dimensional geometrical mapping and reconstruction of the endocardial surface are known in the art. For example, U.S. Pat. No. 5,738,096, whose disclosure is incorporated herein by reference, describes methods for mapping the endocardium based on bringing a probe into contact with multiple locations on a wall of the heart, and determining position coordinates of the probe at each of the locations. The position coordinates are combined to form a map of at least a portion of the heart. These methods are effective and accurate, but they require substantial time and skill to carry them out.
A variety of methods have been developed for non-contact reconstruction of the endocardial surface using intracardial ultrasonic imaging. These methods typically use a catheter with a built-in, miniaturized ultrasonic imaging array or scanner. For example, PCT patent publication WO00/19908, whose disclosure is incorporated herein by reference, describes a steerable transducer array for intracardial ultrasonic imaging. The array forms an ultrasonic beam, which is steered in a desired direction by an active aperture. Similarly, U.S. Pat. No. 6,004,269, whose disclosure is also incorporated herein by reference, describes an acoustic imaging system based on an ultrasound device that is incorporated into a catheter. The ultrasound device directs ultrasonic signals toward an internal structure in the heart to create an ultrasonic image.
Further examples of intracardial ultrasonic imaging are presented in U.S. Pat. NO. 5,848,969 and in PCT patent publication WO98/18388, whose disclosures are incorporated herein by reference. These publications describe systems and methods for visualizing interior tissue regions using expandable imaging structures. The structures assume an expanded geometry once inside the heart, which stabilizes an associated imaging probe or array.
U.S. Pat. No. 5,797,849 and PCT patent publication WO99/58055, whose disclosures are also incorporated herein by reference, describe methods for carrying out medical procedures using a three-dimensional tracking and imaging system. The position of a catheter or other probe inside the body is tracked, and its location relative to its immediate surroundings is displayed to improve a physician""s ability to precisely position it. Various procedures using such a probe are described in these publications. One such procedure is ultrasonic imaging, using an ultrasound imaging head with transducers held outside the body to image an area inside the body in which a probe with a position sensor is located.
Various methods are known in the art for enhancing ultrasonic images and for extracting information, such as three-dimensional contours, from such images. These methods typically combine information from multiple two-dimensional images to define three-dimensional features. For example, PCT patent publication WO99/55233, whose disclosure is incorporated herein by reference, describes a method for defining a three-dimensional surface of at least a portion of a patient""s heart using a plurality of images in different planes. The images are made using an ultrasound transducer at known positions and orientations outside the patient""s body. Anatomical landmarks are manually identified in the plurality of images. Other methods of contour extraction and three-dimensional modeling using ultrasonic images are described in European patent application EP 0 961 135 and in Japanese patent application JP 9-285465 whose disclosures are also incorporated herein by reference. As another example, PCT patent publication WO98/46139, whose disclosure is incorporated herein by reference, describes a method for combining Doppler and B-mode ultrasonic image signals into a single image using a modulated nonlinear mapping function.
It is an object of some aspects of the present invention to provide improved methods and apparatus for three-dimensional mapping and geometrical reconstruction of body cavities, and particularly of chambers of the heart.
In preferred embodiments of the present invention, a cardiac catheter comprises a plurality of acoustic transducers distributed longitudinally along a distal portion of the catheter. The transducers are actuated individually, in sequence, to emit acoustic waves, preferably ultrasonic waves, while the catheter is inside a chamber of the heart. The acoustic waves are reflected from the endocardial surface of the cavity and are received by the transducers. Processing circuitry, coupled to the transducers, determines the times of flight of the received acoustic waves, thus providing a measurement of the distance from each of the transducers to a point or area on the endocardial surface opposite the transducer. The distance measurements are combined to reconstruct the three-dimensional shape of the surface, which is preferably displayed in the form of a geometrical map.
Preferred embodiments of the present invention thus enable the entire endocardial surface to be mapped rapidly, typically within a single heart beat. This rapid mapping can be achieved because the acoustic waves are used to measure three-dimensional distances directly, rather than attempting to image the heart and then extract geometrical information from the images as in methods known in the art. The distance measurements are facilitated by the unique design of the catheter, wherein the transducers are distributed longitudinally along the catheter, instead of being concentrated in a phased array or other imaging configuration. Preferred embodiments of the present invention also avoid the need for physical contact between the catheter and the endocardial surface during measurement.
In some preferred embodiments of the present invention, the catheter comprises one or more position sensors, which are used to determine position and orientation coordinates of the catheter within the heart. Using the position sensors in conjunction with the acoustic measurements allows the reconstructed three-dimensional shape of the surface to be located and oriented in space. It also enables multiple measurements to be taken at different positions within the heart in order to enhance the accuracy of the reconstruction. Preferably, the position sensors comprise one or more miniature coils, which are used to determine position and orientation coordinates by transmitting or receiving electromagnetic waves, as described, for example, in PCT patent publication WO96/05768 or in U.S. Pat. No. 5,391,199, which are incorporated herein by reference. Alternatively, the acoustic transducers on the catheter also serve as position sensors, by receiving acoustic waves transmitted from a plurality of acoustic transducers at fixed positions outside the body, or by transmitting acoustic waves to these external transducers. The times of flight of these waves are used to determine the position and orientation of the catheter. Further alternatively, other types of position sensing systems, as are known in the art, may be used.
In further preferred embodiments of the present invention, the catheter comprises a plurality of electrodes in addition to the acoustic transducers, and is used for electrical, as well as geometrical, mapping of the heart. Preferably, the electrical mapping is performed rapidly using an array of non-contact electrodes, most preferably as described in a U.S. patent application entitled xe2x80x9cRapid Mapping of Electrical Activity in the Heart,xe2x80x9d filed Jun. 21, 2000 (applicant""s docket no. BIO 97 US), which is assigned to the assignee of the present patent application and is incorporated herein by reference. The electrical and geometrical maps are registered to provide an integrated view of mechanical and electrical properties of the heart.
In some preferred embodiments of the present invention, other features of the acoustic waves received by the transducers on the catheter are analyzed to provide further geometrical and diagnostic information. For example, in one such embodiment, the processing circuitry analyzes the reflected waves to find reflections from both the endocardial and the epicardial surfaces. In this manner, both of the surfaces can be reconstructed simultaneously, and the thickness of the heart wall can be mapped.
In another embodiment, the processing circuitry analyzes the frequency, as well as the time of flight, of the reflected waves in order to detect a Doppler shift. The Doppler measurement is used to determine and map the heart wall velocity. This method thus enables the relative speeds of opposing or mutually-perpendicular segments of the heart wall to be measured simultaneously. By contrast, methods of echo Doppler measurement known in the art use a probe outside the body and therefore can measure wall velocity of only one side of the heart at any given time.
Although preferred embodiments are described herein with reference to cardiac catheters for mapping chambers of the heart, other applications of the present invention will be apparent to those skilled in the art. These applications include, but are not limited to, mapping and geometrical reconstruction of other body cavities, such as the coronary arteries or the gastrointestinal system.
There is therefore provided, in accordance with a preferred embodiment of the present invention, apparatus for mapping a surface of a cavity within a body of a subject, including:
an elongate probe, having a longitudinal axis and including a distal portion adapted for insertion into the cavity; and
a plurality of acoustic transducers, distributed along the longitudinal axis over the distal portion of the probe, which transducers are adapted to be actuated individually to emit acoustic waves while the probe is in the cavity, and are further adapted to receive the acoustic waves after reflection of the waves from the surface of the cavity and to generate, responsive to the received waves, electrical signals indicative of times of flight of the waves.
Preferably, the cavity includes a chamber of the heart of the subject, and the probe includes an intracardiac catheter.
Additionally or alternatively, the probe includes a position sensor, which is adapted to generate signals indicative of position coordinates of the probe within the body. Preferably, the position sensor includes a coil, and wherein the signals include electrical currents induced in the coil by an externally-applied magnetic field.
Preferably, the apparatus includes control circuitry, adapted to actuate the transducers sequentially and to receive and to process the electrical signals generated by the transducers so as to reconstruct a three-dimensional shape of the surface of the cavity based on the times of flight. Further preferably, responsive to the times of flight, the circuitry is adapted to determine distances from the transducers to respective points on the surface of the cavity opposite the transducers, and to combine the determined distances so as to reconstruct the shape. Additionally or alternatively, the circuitry is operative to distinguish the signals generated responsive to the waves that have undergone one reflection from the surface of the cavity from the signals generated responsive to the waves that have undergone multiple reflections, and to reject the signals due to the waves that have undergone the multiple reflections.
Preferably, the cavity has a wall, and the surface includes an inner surface of the wall and an outer surface of the wall, and the circuitry is adapted to distinguish the signals generated responsive to the waves that have been reflected from the inner surface from the signals generated responsive to the waves that have been reflected from the outer surface. In a preferred embodiment, the circuitry is operative to determine a thickness of the wall responsive to the signals generated by the waves that have been reflected from the inner surface and the waves that have been reflected from the outer surface.
In another preferred embodiment, the circuitry is adapted to detect a spectral shift in the acoustic waves received by the transducer and to determine, responsive to the spectral shift, a velocity of motion of the surface.
In still another preferred embodiment, the apparatus includes one or more electrodes disposed on the distal portion of the probe, which are adapted to convey electrical signals to the circuitry responsive to electrical activity in the cavity, wherein the circuitry is adapted, responsive to the signals from the electrodes, to superimpose an indication of the electrical activity on the three-dimensional shape of the surface. Preferably, the indication of the electrical activity includes a map of electrical potentials at the surface of the cavity, which is registered with the three-dimensional shape of the surface. Preferably, the apparatus includes a display, which is driven by the circuitry to display an image of the three-dimensional shape.
In a preferred embodiment, the apparatus includes a plurality of reference transducers outside the body, which are adapted to transmit acoustic waves into the body, such that the waves are received by the transducers on the probe, causing the transducers to generate electrical reference signals, and the circuitry is adapted to process the reference signals so as to determine position coordinates of the probe. Preferably, responsive to the determined position coordinates, the circuitry is adapted to define a position of the three-dimensional shape within the body.
In a preferred embodiment, the apparatus includes one or more electrodes disposed on the distal portion of the probe, which are adapted to detect electrical activity in the cavity, wherein the electrical activity detected by the one or more electrodes includes varying electrical potentials at the surface of the cavity. Preferably, the one or more electrodes include an array of non-contact electrodes, which are adapted to detect the varying electrical potentials at the surface substantially without making contact with the surface.
There is also provided, in accordance with a preferred embodiment of the present invention, a method for mapping a surface of a cavity within a body of a subject, including:
inserting a probe into the cavity, the probe having a longitudinal axis; sequentially emitting acoustic waves within the cavity from each of a plurality of points distributed along the longitudinal axis of the probe;
receiving the acoustic waves at the points following reflection of the emitted waves from the surface of the cavity;
analyzing the received waves to determine times of flight of the waves; and
reconstructing a three-dimensional shape of the surface of the cavity based on the determined times of flight.
Preferably, the method includes determining position coordinates of the probe inside the body, wherein reconstructing the three-dimensional shape includes reconstructing the shape responsive to the coordinates, and wherein reconstructing the shape includes defining a position of the shape inside the body using the coordinates. Additionally or alternatively, emitting and receiving the waves include emitting and receiving the waves at a plurality of different locations of the probe in the cavity, and reconstructing the shape includes reconstructing the shape based on the waves received at the different locations, using the coordinates of the probe determined at the different locations.
Alternatively, emitting and receiving the waves include emitting and receiving the waves while the probe is held substantially stationary at a single location in the cavity, and reconstructing the three-dimensional shape includes reconstructing the shape based substantially only on the waves received at the single location.
In a preferred embodiment, the method includes sensing electrical activity in the cavity using electrical sensors on the probe, wherein reconstructing the shape includes superimposing an indication of the electrical activity on the reconstructed three-dimensional shape of the surface.
The present invention will be more fully understood from the following detailed description of the preferred embodiments thereof, taken together with the drawings in which: